tests: _fail on _scratch_mkfs_sized failure

tests: _fail on _scratch_mkfs_sized failure

If _scratch_mkfs_sized() fails, e.g. due to an FS not supporting the
provided size, tests may subsequently mount and run atop a previously
created (e.g. non-size-bound) filesystem.
This can lead to difficult to debug failures, or for some -ENOSPC
exercising tests, near infinite runtimes. Avoid this by renaming the
current function to _try_scratch_mkfs_sized() and _fail in the parent
_scratch_mkfs_sized() wrapper.

[zlang: change _fail output, remove missed _fail in b/007, fix g/466]

Suggested-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: David Disseldorp <ddiss@suse.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Zorro Lang <zlang@kernel.org>